It is known to control the “slump” or fluidity property of concrete in ready-mix delivery trucks by using sensors to monitor the energy required for rotating the mixing drum, such as by monitoring the torque applied to the drum by measuring hydraulic pressure (see e.g., U.S. Pat. Nos. 4,008,093, 5,713,663).
A hydraulic sensor coupled to the hydraulic drive and/or a rotational speed sensor, for example, may be used for monitoring mixing drum rotation. The monitoring of concrete slump involves calibrating the outputs or values obtained from the hydraulic sensor and/or electrical sensor on a mixing truck containing a concrete mix and correlating these with slump values obtained using a standard slump cone test. In the standard slump cone test, a 12-inch truncated cone containing the fresh concrete is removed to permit the concrete to drop, and the vertical height drop of the concrete is measured (e.g. ASTM C143-05). Concrete having this known slump value is added into the drum mixer so that a hydraulic or electrical value, which is obtained as an output from the sensor, can be stored into a memory location and subsequently correlated by computer processing unit (CPU).
During the delivery of the concrete to a customer, the concrete stiffens with time as a result of hydration, evaporation, and other factors, and the sensors detect this as increased hydraulic or electrical energy required for turning the mixing drum. The on-board CPU compares the detected energy value obtained from the sensor or sensors and compares this to values stored in memory. If the sensors and CPU detect that the concrete is beginning to stiffen, the theory is that the CPU can be triggered to activate metering or pumping devices to inject water or other liquid (e.g., chemical dispersant) into the concrete to restore the slump to the desired value.
It has long been desired to obtain the capability to add water or chemical admixture to the concrete in an efficient way, or, in other words, to add the precise quantity of admixture needed to achieve the target rheology value while avoiding dosing errors and lengthy trial and error. The presumption has been that because highly sophisticated sensors and CPU can be used, then an accurate and efficient methodology would inevitably result. However, prior art cement mixing systems, for all of their evolving sophisticated hardware, remain subject to variation in the mixture which they control.
U.S. Pat. No. 5,713,663 of Zandberg et al. declared that slump readings could be monitored in ready-mix trucks by inputting information to an in-line CPU and that such information could include the batch water amount, the amount of particulate material ingredients, sand moisture content, time, “nominated” slump, and other factors (See col. 8, lines 3-14). It was not specifically explained by Zandberg et al., however, which of these factors were to be included or how they were to be weighted. The patent stated that such information could be stored into memory such that the CPU could calculate from the inputted information the required liquid component needed to arrive at a desired slump. It was alternatively explained that the required liquid component could be “pre-calculated” and loaded into the CPU with the other information (Col. 8, lines 15-22). The patent further mentioned that the memory may have stored information “in a look-up table” related to “a range of possible mixes” and thus “for particular mix types and particular slump values and particular amounts of mix ingredients, the system will be able to compare measured values by the sensors against known values for the mix to provide for an adjustment either manually or automatically of the liquid component which is added” (Col. 8, lines 29-36).
Despite reiterating that the objective was to enable “maximization of mixing without an over-supply of liquid component” which otherwise required the concrete mix to be returned rather than delivered, Zandberg et al. did not specify what factors were to be included in the “look-up” table. Nor did they set forth the precise methodology for calculating the dose of the liquid component to be administered.
Similarly, U.S. Pat. Nos. 6,042,258 and 6,042,259 of Hines et al. (MBT Holding/BASF) disclosed an admixture dispensing system for stabilizing the concrete either overnight, same day (as delivery), or for long haul operations. In each of these modes, admixture doses were to be calculated based on “internal charts” located within computer-accessible memory (See e.g., U.S. Pat. No. 6,042,258 at Col. 9, lines 4-30; at Col. 9, lines 42-52; at Col. 10, lines 7-20; and also FIG. 2A at 128, 138, and 148). However, the number of “variables” or conditions required for inclusion on such internal charts or tables appeared to be rather extensive. These variables included the amount of concrete in the mixer, its temperature, the type of cement in the concrete, the amount of time that the concrete is to be in transit in the delivery truck), the amount of water required, and other factors. It was suggested that a batchman or driver may generate his own specific charts or look-up tables depending on the data chosen for entry into the computer, and that the software provider could make adjustments allowing for the driver or batchman “to compensate dosage values for factors not considered in the data charts or look-up tables” (See e.g., U.S. Pat. No. 6,042,258 at col. 9-10; See also U.S. Pat. No. 6,042,259 at col. 9-10). Furthermore, it should be emphasized that the intent of adding admixture was to control cement hydration, rather than slump or other rheology value.
In US Patent Publication 2009/0037026, Sostaric et al. (RS Solutions LLC) disclosed a system for adjusting concrete in ready-mix delivery vehicles using water or chemical additives. This system included sensors for detecting various parameters: such as temperature, pressure, rotation (speed, energy), and tilt/acceleration for calculating slump (See e.g., FIG. 4C; Para. 0071-0072). For example, the system could include sensors for measuring load temperature as well as skin temperature of the mixing drum. The system could also include sensors for measuring “acceleration/deceleration/tilt.” The system could even include sensors for measuring vibration and environmental parameters, such as humidity and barometric pressure. (See paragraph 0132). Moreover, the system would automatically add water or other admixtures based upon the measured output of the sensors used by the system.
Despite increased technological sophistication for measuring the ever-increasing number of parameters, as suggested by the increasing number of sensors being deployed for measuring various aspects of the cement during its delivery to a construction site, the present inventors do not believe that the current state of the prior art provides clear guidance about which parameters must be considered and included in lookup tables or which parameters are most important for calculating chemical admixture dosing amounts.
Achieving accurate and efficient dosing of chemical admixtures into concrete is presumed to be difficult in large part due to the fact that the effect of added chemical admixtures on rheology is altered to a greater extent than that of water on rheology by the proportions (e.g. water to cement ratio), characteristics (e.g. cement fineness), and condition (e.g. temperature) of the concrete ingredients and history of the load (age, temperature profile, etc.). These factors are likely to change over the course of different loads of concrete batched over the course of a day, week, month, etc. For instance, the concrete temperature may increase with each batch during the day as the ambient temperature increases. Different deliveries of cement may vary in chemistry and fineness.
Rather than just adjusting slump, it is desired to adjust other rheological properties of the concrete. Rheology deals with the science of the flow and deformation of matter. The rheology of concrete can be defined in terms of slump, slump flow, yield stress, plastic viscosity, apparent viscosity, thixotropy, or flow table test, among other factors. Therefore it is an object of this invent to select the proper dose of chemical admixture to adjust one or more of such concrete rheology parameters.
In view of the foregoing, the present inventors believe that a novel method for adjusting concrete rheological properties in mixing drums and other mixing devices is needed, a method that is more efficient and practical to use than ones in current practice.